CN103913789A - Method for preparing high aspect ratio metal microgratings on metal substrate - Google Patents

Abstract

The invention discloses a method for preparing metal micro-gratings with a high aspect ratio on a metal substrate, which belongs to the technical field of micro-manufacturing. Using UV-LIGA technology on the high-purity nickel plate substrate J, the SU-8 adhesive film was obtained through two photolithography processes such as uniform coating, layered exposure, and one-time development, and then processed by micro-electroforming nickel N and micro-electroforming To realize the production of metal micro-grating; through the method of line width compensation to solve the problem of shrinking line width caused by swelling; Vacuum annealing is used in the process to remove residual stress and improve the bonding force between the substrate and the metal grating. The effects and benefits of the present invention are: the metal micro-grating prepared on the metal substrate J by this method has the characteristics of high aspect ratio, dimensional accuracy and high mechanical strength, and the preparation process is simple and the cost is low.

Description

Method for preparing metal micro-grating with high aspect ratio on metal substrate

technical field

The invention belongs to the technical field of micro-manufacturing, and relates to metal substrate micro-electroforming metal devices, in particular to a method for preparing a high-aspect-ratio metal micro-grating on a metal substrate based on a UV-LIGA process.

Background technique

As one of the core unit devices of optical instruments, metal micro-gratings have important applications in many fields such as spectral measurement, optical computing, and optical information processing. As the demand for metal micro-gratings continues to grow, its processing and preparation methods have attracted more and more attention from researchers. The existing metal micro-gratings are mainly prepared by using silicon as the substrate and combining sputtering, masking layer preparation, etching and other processes. For example, pages 296-298 of the 2010 Proceedings of "Function and Materials" and pages 154-159 of "Journal of Infrared and Millimeter Waves", Volume 32, Issue 2, April 2013. Document 1 firstly sputtered a layer of aluminum film on Si, then combined with photolithography to prepare a masking layer, and finally prepared an aluminum grating with a period of 8 μm and a height of 0.3 μm by wet etching the aluminum film. But the metal grating prepared by this method is limited in height. Document 2 firstly spin-coats a cycloolefin polymer (COP) film on a silicon wafer substrate, then imprints a grating structure, and then sputters an Au film to form a composite structure of COP and Au, and then uses a mixed gas of Ar and CF ₄ The gold on the upper surface was etched, and then the residual COP layer was etched with oxygen reactive ions, and finally a gold grating with a maximum height of 1 μm was prepared. However, the side wall of the grating prepared by this method is inclined, the height is limited, the process is complicated, and the cost is relatively expensive. In addition, both of them use fragile silicon wafers as the substrate, which is prone to failure due to the cracking of the substrate during the preparation process.

Metal micro-gratings prepared by UV-LIGA process with metal as the substrate have the characteristics of high aspect ratio, dimensional accuracy and mechanical strength, and the preparation process is simple and the cost is low. The prepared metal micro-gratings with high aspect ratio have broad application prospects.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a metal micro grating with a high aspect ratio on a metal substrate based on a UV-LIGA process. The technical scheme adopted in the present invention is to obtain the SU-8 adhesive film on the substrate of high-purity nickel plate through two photolithography processes such as uniform glue, layered exposure, and one development, and then micro-electroforming nickel and micro-electroforming post-processing. Realize the production of metal micro-grating; through the method of line width compensation to solve the problem of line width reduction caused by swelling; Vacuum annealing is used to remove residual stress.

Specific steps are as follows:

(1) Substrate pretreatment: First, the nickel substrate was ground and polished to make its surface roughness less than 0.04 μm, then the surface of the substrate was wiped clean with acetone cotton balls, followed by ultrasonic cleaning in acetone and ethanol respectively, and then pure After rinsing with water, blow dry, and finally bake in an oven, remove moisture and cool to room temperature;

(2) Preparation of SU-8 film: use a desktop coater to spin-coat SU-8 photoresist twice on the substrate, and set different speeds on the coater to obtain films of different thicknesses; The SU-8 photoresist is developed after standing, pre-baking, exposure, and post-baking, and finally the required SU-8 film is obtained; the obtained film is directly used as a mold for micro-electroforming;

(3) Micro-electroforming: adopt the no-backing growth process of direct electroforming growth on the metal substrate; during the electroforming process, cathode movement and circulation filtration are applied; the electroforming solution formula is: nickel sulfamate 365-375g/L , nickel chloride 6~10g/L, boric acid 55~60g/L; micro-electroforming nickel process conditions: pH value 3.9~4.1, temperature 48℃~52℃, current density 0.5~1A/dm ² ;

(4) Manual grinding and polishing: Grinding and polishing the surface of the electroforming layer after electroforming by manual grinding to obtain a flat surface of the electroforming layer;

(5) Remove SU-8 glue: First, soak the substrate with grating structure in SU-8 degumming solution at 80-90°C, soak for 5-10 hours, apply ultrasound for 1-2 hours, then remove the ultrasonic and continue to use the degumming solution Soaking, such a cycle of "soaking-ultrasonic-soaking-ultrasonic" to remove glue, finally get a clean grating structure;

(6) High-temperature vacuum annealing: the absolute vacuum degree of annealing is about 10 ^-3 Pa, the temperature is 350-400°C, the annealing time is 1-1.5h, and then cooled with the furnace.

The beneficial effect of the invention is that it solves the problems of limited etching depth, fragile substrate, difficult control of etching precision and the like in the existing method for preparing metal micro-gratings on the silicon substrate. The metal micro-grating prepared on the metal substrate by this method has the characteristics of high aspect ratio, dimensional accuracy and high mechanical strength, and the preparation process is simple and the cost is low. According to the specific requirements of users, metal micro-gratings with a high aspect ratio with a height of several hundred microns and low internal stress in the micro-electroforming layer can be prepared; it can provide metal micro-gratings with low surface roughness for the field of micro-manufacturing.

Description of drawings

Figure 1 Schematic diagram of the grating structure.

Figure 2 The first layer of SU-8 glue.

Figure 3 First exposure.

Figure 4 The second layer of SU-8 glue.

Figure 5 Second exposure.

Figure 6 Development effect diagram.

Figure 7 Micro-electroformed nickel.

Figure 8 SU-8 glue removal effect diagram.

In the figure: S1 and S2 are SU-8 photoresist films, A is free space, N is nickel metal, and J is substrate.

Detailed ways

The specific implementation manners of the present invention will be described in detail below in combination with the above technical solutions and accompanying drawings.

For example, a metal micro-grating with high aspect ratio is prepared on a high-purity nickel plate with a nickel content of 99.99%, as shown in Figure 1, and its comprehensive dimensions are as follows: the width of the grating boss is 65 μm, the length is 900 μm, the height is 243 μm, and the grating period is 130 μm . The size of the nickel plate is 60×20×3mm ³ , and the specific steps for preparing the structure are as follows:

(1) Substrate pretreatment: Grind and polish on a grinding and polishing machine first, and finally the surface roughness of the nickel substrate reaches below 0.04 μm; then wipe the substrate surface with acetone cotton balls, and then perform ultrasonic cleaning in acetone and ethanol respectively After 10 minutes, rinse with pure water and blow dry, and finally bake in an oven at 120°C until the water vapor is removed and then cool to room temperature.

(2) Preparation of SU-8 adhesive film: Spin coat the first layer of SU-8 photoresist S1 on the front of the substrate J using a desktop homogenizer (as shown in Figure 2). ~170μm; then let it stand on a horizontal table for 30min; then pre-baked at a temperature of 85-95°C for 1-2h, and cooled with the furnace; the next exposure was to use SU-8 glue sensitive 365nm on the exposure machine The ultraviolet light of the wavelength is exposed by the method of contact exposure, the exposure power density is 10-13mW/cm ² , and the exposure time is 2-5min, as shown in Figure 3; followed by post-baking, that is, on a hot plate at 85°C Heating up for 3-5 minutes; after cooling, carry out the second spin coating of SU-8 glue, as shown in Figure 4, the rotation speed is 1200-1300rpm, and the thickness of SU-8 photoresist S2 glue is 110-130μm; The steps of standing still, pre-baking, exposure (as shown in Figure 5) and post-baking are the same as above; finally, develop with SU-8 developer for 10-20 minutes to obtain a clean SU-8 film, as shown in Figure 6.

(3) Micro-electroforming nickel: a back-plate-free growth process that directly electroforms and grows on the substrate is adopted. During the electroforming process, cathode movement and circulation filtration are applied. The electroforming liquid formula is: nickel sulfamate: 365-375g/L, nickel chloride: 6-10g/L, boric acid: 55-60g/L; Nickel process conditions are: PH value: 3.9-4.1, temperature: 48°C-52°C, current density: 0.5-1A/dm ² . The micro-electroforming nickel process is to deposit metallic nickel N into the free space A of the micro-electroforming mold, as shown in FIG. 7 .

(4) Manual grinding and polishing: use 2000# sandpaper for manual grinding, use a polishing paste with a particle size of 2.5-3.0 μm for polishing, and the total removal amount is 5-20 μm;

(5) Remove SU-8 glue: First, soak the substrate with grating structure in SU-8 degumming solution at 80-90°C, soak for 5-10 hours, apply ultrasound for 1-2 hours, then remove the ultrasonic and continue to use the degumming solution Soaking, such "soaking-ultrasonic-soaking-ultrasonic" cycle to remove glue, finally get a clean grating structure, as shown in Figure 8.

(6) High-temperature vacuum annealing: the absolute vacuum degree of annealing is about 10 ^-3 Pa, the temperature is 350-400°C, the annealing time is 1-1.5h and then cooled in the furnace.

The average height of the final nickel metal micro-grating is 245.6 μm, and its relative error is 1%; the average period of the grating is 130.4 μm, and the relative error is 0.3%; the average line width of the grating boss is 65.5 μm, and the relative error is 0.7%; The upper surface roughness reaches 4.6nm.

Claims (1)

1. in metallic substrates, prepare the method for high-aspect-ratio metal low-light grid, be included in high-purity nickel substrate, through twice even glue, layering exposure and once the photo-etching technological process such as development obtain SU-8 glue glued membrane, more micro-electroformed nickel, micro-electroforming aftertreatment realize the making of metal low-light grid; The method compensating by live width solves the swelling line widths shrink problem causing; Removing photoresist in operation, adopt the method that " ultrasonic-to soak-ultrasonic-to soak " moves in circles to remove photoresist; In annealing operation, use vacuum annealing to remove unrelieved stress; Concrete steps are as follows:

(1) substrate pre-service: first, ni substrate makes its surfaceness be less than 0.04 μ m through grinding, polishing, then use acetone cotton balls by substrate surface wiped clean, then in acetone and ethanol, impose ultrasonic cleaning respectively, after clean by pure water rinsing again, dry up, finally in baking oven, cure, after removal steam, be cooled to room temperature;

(2) preparation of SU-8 glue glued membrane: use desk-top sol evenning machine spin coating SU-8 photoresist at twice in substrate, sol evenning machine arranges different rotating speeds and obtain the glued membrane of different-thickness; The SU-8 photoresist of gradation spin coating respectively through leaving standstill, front baking, exposure, after once develop after drying, finally obtain required SU-8 glue glued membrane; The glued membrane obtaining is directly as the pattern of micro-electroforming;

(3) micro-electroforming: adopt the no backing process that directly electroforming is grown in metallic substrates; In electroforming process, impose movable cathode and circulating filtration; Formulation of electroforming solution is: nickel sulfamic acid 365～375g/L, nickel chloride 6～10g/L, boric acid 55～60g/L; Micro-electroformed nickel process conditions are: pH value 3.9～4.1,48 DEG C～52 DEG C of temperature, current density 0.5～1A/dm ²;

(4) underhand polish polishing: grinding and polishing is carried out on the electroformed layer surface after adopting the method for underhand polish to electroforming, to obtain smooth electroformed layer surface;

(5) remove SU-8 glue: first the substrate immersion with optical grating construction is removed photoresist in liquid at the SU-8 of 80～90 DEG C, soak the after-applied ultrasonic 1～2h of 5～10h, remove afterwards the ultrasonic glue immersion that continues to spend, so " soak-ultrasonic-soak-be ultrasonic " and move in circles and remove photoresist, finally obtain clean optical grating construction;

(6) high-temperature vacuum annealing: annealing Absolute truth reciprocal of duty cycle is about 10 ^-3pa, temperature is 350～400 DEG C, annealing time 1～1.5h is then cooling with stove.